DHODH is a protein that catalyzes one of the steps in denovo pyrimidine nucleotide biosynthetic pathway. (Greene et al. Biochem Pharmacol 1995, 50:861-7; Davis J. P et al. FASEB J 1996, 10(6): Abst C23). It catalyzes the only oxidation/reduction reaction in that pathway, which is the step of converting DHO (dihydroorotate) to orotate with the aid of flavin cofactor and an electron acceptor. Inhibitors of dihydroorotate dehydrogenase have been found to possess wider applications as chemotherapeutic agents. (Kensler et al. 1989 in: Design of Enzyme Inhibitors as Drugs; Sandler, M., and Smith, H. J. Eds., pp 379-401 Oxford Univ Press, Oxford England; Cody et al. Am. J. Clin. Oncol. 16, 526-528 (1993)).
As an example for DHODH inhibitors, the quinoline derivative Brequinar (6-Fluoro-2-(2′-fluoro[1,1′-biphenyl]-4-yl)-3-methyl-4-quinolinecarboxylic acid) exhibits an anticancer activity towards L1210 murine leukemia (Andreson L W. Et al. Cancer Commun. 1989; 1(6), 381-7; Chen S F. et al. Cancer Res. 1986 October; 46(10): 5014-9). It has also been shown that Brequinar potentiates 5-fluorouracil antitumor activity in a murine model colon 38 tumor by tissue-specific modulation of uridine nucleotide pools. (G Pizzorno et al. Cancer Res. 1992 Apr. 1; 52:1660-5).
DHODH inhibitors may also be useful in the treatment of viral mediated diseases (see U.S. Pat. No. 6,841,561). Furthermore, inhibition of DHODH is known to be among promising target for treating transplant rejection, rheumatoid arthritis, psoriasis as well as autoimmune diseases (Kovarik, J. M. et al. Expert Opin. Emerg. Drugs 2003, 8, 47; Allison, A. C. Transplantation Proc. (1993) 25(3) Suppl. 2, 8-18); Makowka, L., Immunolog Rev. (1993) 136, 51-70; Davis J. P et al. Biochemistry 1996, 35: 1270-3).
Leflunomide, a well known DHODH inhibitor is a synthetic drug currently marketed, a low-molecular weight drug of the isoxazole class (see EP0527736, JP1993506425, JP1999322700, JP1999343285, U.S. Pat. No. 5,494,911, U.S. Pat. No. 5,532,259, WO19991017748) and used in the treatment of Rheumatoid arthritis and is also under evaluation for use in the treatment of inflammatory bowel disease and chronic allograft rejection.
In vivo, Leflunomide is quickly transformed in its active metabolite Teriflunomide that exerts its anti-inflammatory, antiproliferative and immunosuppressive effects via mechanisms that are not completely understood. Teriflunomide is not only a potential inhibitor of protein tyrosine kinase in vivo but a 100-1,000-fold greater inhibitor of DHODH (Davis J. P et al. FASEB J 1996, 10(6): Abst C23; Davis J. P et al. Biochemistry 1996, 35:1270-3).
With the rise in number of patients affected by autoimmune and related diseases, there is unmet need for new drugs that can treat such diseases more effectively. There is still a crucial need for immunosuppressive agents, that are further useful in a wide variety of autoimmune and chronic inflammatory diseases, including systemic lupus erythematosus, chronic rheumatoid arthritis, multiple sclerosis, type I diabetes mellitus, inflammatory bowel diseases, biliary cirrhosis, uveitis and other disorders such as Crohn's diseases, ulcerative colitis, bullous pemphigoid, sarcoidosis, psoriasis, autoimmune myositis, Wegener's granulomatosis, ichthyosis, Graves ophthalmopathy, atopic dermatitis and asthma. They may also be useful as part of chemotherapeutic regimens for the treatment of cancers, lymphomas and leukemias, alone or in combination with antitumoral compounds well known by the one skilled in the art.